Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Auto Selective Serial Interface

IP.com Disclosure Number: IPCOM000111398D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Kurishita, Y: AUTHOR [+2]

Abstract

This article describes an Auto-Selective Serial Interface circuit which can select RS-232 interface or RS-422 interface automatically by sensing and monitoring a signal level of each line. This circuit enables automatic interface switching between each interface without operating a mechanical switch or mechanical connection change.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 81% of the total text.

Auto Selective Serial Interface

      This article describes an Auto-Selective Serial Interface
circuit which can select RS-232 interface or RS-422 interface
automatically by sensing and monitoring a signal level of each line.
This circuit enables automatic interface switching between each
interface without operating a mechanical switch or mechanical
connection change.

      The Figure shows the concept of this circuit.  The RS-232
signal level has "Space" state (up +2 volts) or "Mark" state (under
-2 volts).  When the RS-232 serial interface is connected, the
RxD(Receive Data) signal line on the interface is in the Mark state
when there is no communication, and it has one Mark state at least in
every one data frame when communicating.  So by sensing this RxD
signal level, the connected serial interface can be judged whether it
is connected to the RS-232 interface or the RS-422 interface.

      Level Sense circuit (1) detects whether the RxD signal is in
the Mark state (under -2 volts) or not.  The Delay Circuit or Timer
circuit (2) is needed for judgment when communicating.  As described
above, RxD signal has one Mark state at least in every one data frame
when communicating.  So the RxD signal must be monitored whether it
has one Mark state during one data frame span.  This circuit (2) is
used for this function.  SW (3) is a switch which is used for
selecting receive data from either RS-232 or RS-422.  When the RS-232
interface is connected, the rec...